Manufacturing of decorative surfaces

ABSTRACT

A method for manufacturing decorative surfaces includes, in order, the steps of a) inkjet printing an image on a first thermoplastic foil by jetting and UV curing one or more pigmented free radical UV curable inkjet inks on the first thermoplastic foil; b) applying on the inkjet printed image a second thermoplastic foil carrying a layer containing a vinylchloride-vinylacetate-vinylalcohol copolymer with the layer facing the inkjet printed image on the first thermoplastic foil; and c) heat pressing the first and second thermoplastic foils into a decorative laminate; wherein at least one of the first and second thermoplastic foils is transparent, and the one or more pigmented free radical UV curable inkjet inks contain a polymerizable composition having: 30 to 90 wt % of one or more compounds with one ethylenically unsaturated polymerizable group; 10 to 70 wt % of one or more compounds with two ethylenically unsaturated polymerizable groups; and 0 to 10 wt % of one or more compounds with three or more ethylenically unsaturated polymerizable groups.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2017/074341, filed Sep. 26, 2017. This application claims thebenefit of European Application No. 16191676.2, filed Sep. 30, 2016,which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to the manufacturing of decorativesurfaces, preferably decorative panels or tiles, using inkjettechnology. The invention relates in particular to decorative panels ofPVC (polyvinyl chloride), also called vinyl tiles or vinyl strips.Often, also the abbreviation LVT is used for such tiles, which standsfor Luxurious Vinyl Tile.

2. Description of the Related Art

Gravure, offset and flexography are being increasingly replaced fordifferent applications by industrial inkjet printing systems, because oftheir flexibility in use, such as variable data printing making shortproduction runs and personalized products possible at low cost, andtheir enhanced reliability, allowing incorporation into productionlines.

EP 2865527 A (AGFA GRAPHICS) discloses a method of manufacturing adecorative surface including the steps of: a) impregnating a papersubstrate with a thermosetting resin; b) jetting a colour pattern withone or more aqueous inkjet inks including a polymer latex binder on thethermosetting resin impregnated paper; c) drying the one or more aqueousinkjet inks; and d) heat pressing the thermosetting paper carrying thecolour pattern into a decorative surface.

A major drawback of these wood- and paper-based decorative panels istheir limited water resistance, which prevents their use in bathroomsand kitchens.

One approach is to use a water-resistant broadloom decorative surface,for example by applying wall-to-wall a PVC flooring roll. However, asthe walls and entrances of rooms generally have multiple corners andindentations, the application of such a large flooring roll requiresexperienced workers and removal of all furniture from the room.

Another approach is to resolve the water resistance issue by replacingwood- and paper-based layers in decorative panels by water resistantpolymeric layers. Such polymeric based floor panels employing polymerslike polyvinyl chloride are disclosed by e.g. WO 2011/077311 A (FLOORINGINDUSTRIES). These polymeric floor panels have interlock structures thatinterlock with similar panels having similar interlock structuresallowing easy do-it-yourself mounting of a glue-free floor surfacecovering. The decorative layer in such floor panels is made by gravureprinting water-based or solvent-based inks having a relatively highviscosity on a thermoplastic foil made of PVC.

Inkjet inks in general have a relatively low viscosity, which causeimage quality problems, e.g. bleeding, when printing water-based orsolvent-based inkjet inks on a thermoplastic foil made of PVC.

The unpublished patent application PCT/EP2016/060507 (AGFA & UNILIN)discloses a method for manufacturing decorative surfaces including thesteps of: a) inkjet printing (19) an image on a first thermoplastic foil(12) using a pigmented UV curable inkjet ink; b) applying a secondthermoplastic foil (12) on the inkjet printed image; and c) heatpressing (20) the first and second thermoplastic foils into a decorativelaminate; wherein the pigmented UV curable inkjet ink contains apolymerizable composition having 30 to 70 wt % of monofunctionalpolymerizable compounds and 30 to 70 wt % of polyfunctionalpolymerizable compounds, wherein the weight percentage wt % is based onthe total weight of the polymerizable composition; and wherein at leastone of the first and second thermoplastic foils is a transparent foil.The decorative panels of the invention exhibit good adhesion and nocracking. However sometimes still higher flexibility is required forhighly curved surfaces, for example, around pillars.

Hence, there is still a need for improved manufacturing methods ofdecorative surfaces using inkjet technology.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention have been realised with a method formanufacturing decorative surfaces as defined below.

The use of specific pigmented UV curable inkjet inks in combination witha specific vinylchloride-vinylacetate copolymer allowed obtainingdecorative panels with excellent image quality, adhesion, highflexibility and no cracking of the print during embossing.

The manufacturing process was made much simpler allowing it to becompletely performed at the facilities of the decorative panelmanufacturer.

One advantage for the decorative panel manufacturer is that the largestock of non-digitally printed decorative rolls could be eliminated asjust-in-time UV inkjet printing was incorporated in the manufacturingprocess. Another advantage of this was that it became possible to reactmuch faster to market trends and that waste of decorative rolls waseliminated as they did not have to be ordered at a decor printer in aminimum purchasing quantity and way in advance.

In-house printing allows for a wide product variety and customizedproducts, e.g. decorative panels including company logo's, and thiswithout substantial financial penalties.

Another advantage of inkjet printing is that the manufacturing processcould be controlled to a level that, for example, an embossed wood grainis in perfect alignment with the inkjet printed wood colour pattern.

Further advantages and embodiments of the present invention will becomeapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the prior art production process for manufacturingpolymeric decorative panels, wherein a PVC roll manufacturer (11)supplies a PVC roll (12) to a decor printer (13) using gravure printing(14) in order to deliver a decorative PVC roll (15) to a warehouse (16)of a floor panel manufacturer (18). The PVC roll manufacturer (11)supplies also PVC rolls (12) to a warehouse (17) of the floor panelmanufacturer (18), who makes an assembly of layers from the PVC roll(12), the decorative PVC roll (15) and a base layer (21) which afterheat-pressing (20) into a single unit are cut into decorative panels(22) that are collected in a decorative panel set (23) ready for sale.

FIG. 2 shows a production process for manufacturing polymeric decorativepanels, wherein a PVC roll manufacturer (11) supplies PVC rolls (12) toa warehouse (15) of a floor panel manufacturer (18), who prepares adecorative PVC roll (15) by inkjet printing (19) on a PVC roll (12). Thefloor panel manufacturer (18) then makes an assembly of layers from thePVC roll (12), the decorative PVC roll (15) and a base layer (21) whichafter heat-pressing (20) into a single unit are cut into decorativepanels (22) that are collected in a decorative panel set (23) ready forsale.

FIG. 3 shows a cross-section of a decorative panel (22) including a baselayer (35) with a tongue (31) and groove (32) laminated on the top sideby a transparent or opaque thermoplastic foil (34) and a transparentthermoplastic foil (33).

FIG. 4 is a photograph of an apparatus for determining flexibility.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Definitions

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. methyl, ethyl, for three carbon atoms:n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl andtertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl,2,2-dimethylpropyl and 2-methyl-butyl, etc.

Unless otherwise specified a substituted or unsubstituted alkyl group ispreferably a C₁ to C₆-alkyl group.

Unless otherwise specified a substituted or unsubstituted alkenyl groupis preferably a C₂ to C₆-alkenyl group.

Unless otherwise specified a substituted or unsubstituted alkynyl groupis preferably a C₂ to C₆-alkynyl group.

Unless otherwise specified a substituted or unsubstituted aralkyl groupis preferably a phenyl or naphthyl group including one, two, three ormore C₁ to C₆-alkyl groups.

Unless otherwise specified a substituted or unsubstituted alkaryl groupis preferably a C₇ to C₂₀-alkyl group including a phenyl group ornaphthyl group.

Unless otherwise specified a substituted or unsubstituted aryl group ispreferably a phenyl group or naphthyl group.

Unless otherwise specified a substituted or unsubstituted heteroarylgroup is preferably a five- or six-membered ring substituted by one, twoor three oxygen atoms, nitrogen atoms, sulphur atoms, selenium atoms orcombinations thereof.

The term “substituted”, in e.g. substituted alkyl group means that thealkyl group may be substituted by other atoms than the atoms normallypresent in such a group, i.e. carbon and hydrogen. For example, asubstituted alkyl group may include a halogen atom or a thiol group. Anunsubstituted alkyl group contains only carbon and hydrogen atoms.

Unless otherwise specified a substituted alkyl group, a substitutedalkenyl group, a substituted alkynyl group, a substituted aralkyl group,a substituted alkaryl group, a substituted aryl and a substitutedheteroaryl group are preferably substituted by one or more constituentsselected from the group consisting of methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl and tertiary-butyl, ester, amide, ether,thioether, ketone, aldehyde, sulfoxide, sulfone, sulfonate ester,sulphonamide, —Cl, —Br, —I, —OH, —SH, —CN and —NO₂.

Manufacturing Methods of Decorative Surfaces

A method for manufacturing decorative surfaces including, in order, thesteps of:

a) inkjet printing (19) an image on a first thermoplastic foil (12) byjetting and UV curing one or more pigmented free radical UV curableinkjet inks on the first thermoplastic foil (12); b) applying on theinkjet printed image a second thermoplastic foil (12) carrying a layercontaining a vinylchloride-vinylacetate-vinylalcohol copolymer with thelayer facing the inkjet printed image on the first thermoplastic foil;and c) heat pressing (20) the first and second thermoplastic foils intoa decorative laminate; wherein at least one of the first and secondthermoplastic foils is a transparent thermoplastic foil; and wherein theone or more pigmented free radical UV curable inkjet inks contain apolymerizable composition having: 30 to 90 wt % of one or more compoundswith one ethylenically unsaturated polymerizable group; 10 to 70 wt % ofone or more compounds with two ethylenically unsaturated polymerizablegroups; and 0 to 10 wt % of one or more compounds with three or moreethylenically unsaturated polymerizable groups, wherein all weightpercentages wt % are based upon the total weight of the polymerizablecomposition.

In a more preferred embodiment, the above method includes a step d) ofcutting the laminate into a decorative panel (22). The method of theinvention can also be used to manufacture broadloom decorative surfaces(e.g. vinyl rolls), but is preferably used for manufacturing decorativepanels, as the latter do not require experienced workers for theirapplication and removal of all furniture from a room.

The foils are thermoplastic so that they can be fused together duringheat-pressing (20). Heat pressing is preferably performed by preheatingthe first and second thermoplastic foils preferably to a temperatureabove 130° C., more preferably between 140 and 170° C., and preferablythen using a cooled press to fuse them into a decorative laminate.Alternatively, the press containing the first and second thermoplasticfoils may be heated to a temperature above 130° C., followed by coolingthe press to fuse the first and second thermoplastic foils into adecorative laminate. The pressure used in both methods is preferablymore than 10 bar, more preferably between 15 and 40 bar.

The thermoplastic foils are preferably selected from the groupsconsisting of polyvinyl chloride (PVC), polyolefins like polyethylene(PE) and polypropylene (PP), polyamides (PA), polyurethane (PU),polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), polymethylmethacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate(PET), polyetheretherketone (PEEK) or mixtures or co-polymers of these.

In a preferred embodiment, the first and second thermoplastic foils arepolyvinyl chloride foils. The polyvinylchloride foils are preferably ofthe rigid type including less than 10 wt % of plasticizer, morepreferably these PVC foils contain 0 to 5 wt % of plasticizer. Theplasticizer may be a phthalate plasticizer, but is preferably anon-phthalate plasticizer for health reasons.

Preferred non-phthalate plasticizers include diisononylcyclohexane-1,2-dicarboxylate (DINCH), dipropylene glycol dibenzoate(DGD), diethylene glycol dibenzoate (DEGD), triethylene glycoldibenzoate (TEGD), acetylated monoglycerides of fully hydrogenatedcastor oil (COMGHA) isosorbide esters, bis-(2-ethylhexyl) terephthalate,vegetable oil based plasticizers like Ecolibrium™ from DOW, and blendsthereof.

In a preferred embodiment, the pigmented UV curable inkjet ink is curedusing UV LEDs.

Decorative Surfaces

Here below the invention will be disclosed for decorative panels, butwith the exception of the tongue and groove profiles, the invention isequally applicable to a broadloom decorative surface, such as a vinylroll.

A decorative panel (22) obtained by the method according to the presentinvention includes an inkjet printed image between two thermoplasticfoils,

wherein at least one of the two thermoplastic foils is a transparentfoil. A transparent foil is necessary to make the inkjet printed imageviewable as it is located on the inside of the decorative laminate.

In a preferred embodiment, the decorative panel (22) includes an inkjetprinted image on a first thermoplastic foil (34), which is preferably anopaque thermoplastic foil, while the second thermoplastic foil (33) istransparent and carries a layer containing avinylchloride-vinylacetate-vinylalcohol copolymer.

In an alternative embodiment, the decorative panel (22) includes aninkjet printed image on a transparent first thermoplastic foil (33),while the second thermoplastic foil (34) is preferably opaque andcarrying a layer containing a vinylchloride-vinylacetate-vinylalcoholcopolymer.

The advantage of having an opaque thermoplastic foil is that the colourvividness of the inkjet printed image is enhanced and that any defectsand irregularities in the optional base layer are masked and thus cannotinfluence image quality. The opaque thermoplastic foil is preferably awhite opaque thermoplastic foil, but may also be a yellowish or brownishopaque thermoplastic foil for reducing ink consumption during inkjetprinting.

In a more preferred embodiment, the decorative panel (22) includes atongue (31) and groove (32) for glue-less interlocking with decorativepanels having a similar tongue and groove. In a more preferredembodiment, the tongue (31) and groove (32) are part of the base layer(35).

Decorative panels including a tongue and a groove of a special shape(see FIG. 3) can be clicked into one another. The advantage thereof is afast and easy assembly of a floor or wall requiring no glue. The shapeof the tongue and groove necessary for obtaining a good mechanical joinis well-known in the art of laminate flooring, as exemplified in EP2280130 A (FLOORING IND), WO 2004/053258 (FLOORING IND), US 2008010937(VALINGE) and U.S. Pat. No. 6,418,683 (PERSTORP FLOORING).

The tongue and groove profiles are especially preferred for flooringpanels and wall panels, but in the case of furniture panels, such tongueand groove profile is preferably absent for aesthetical reasons of thefurniture doors and drawer fronts. However, a tongue and groove profilemay be used to click together the other panels of the furniture, asillustrated by US 2013071172 (UNILIN).

A decorative panel, like a floor panel, has a single inkjet printedimage on a thermoplastic foil. However, an inkjet printed image may alsobe present on both sides of a base layer. The latter is especiallydesirable in the case of decorative panels for furniture. In such acase, preferably the inkjet printed images are located between twothermoplastic foils on both sides of the base layer.

The decorative panels may have any desired shape such as a square, arectangle or an octagon. For flooring, the decorative panels preferablyhave a rectangular shape, for example, 18 cm×140 cm, and a thickness of2 to 6 mm. At a thickness of no more than 6 mm, a large floor surfacecan be covered by a rather limited total weight of decorative panels.The low weight increases comfort when installing the decorative panelsand causes a financial benefit in transport to warehouses compared toheavier wood based decorative panels.

In a preferred embodiment, the decorative panels are made in the form ofrectangular oblong strips. The dimensions thereof may vary greatly.Preferably the panels have a length exceeding 1 meter, and a widthexceeding 0.1 meter, e.g. the panels can be about 1.3 meter long andabout 0.15 meter wide. According to a special embodiment the length ofthe panels exceeds 2 meter, with the width being preferably about 0.2meter or more. The print of such panels is preferably free fromrepetitions.

In a preferred embodiment the decorative panels are selected from thegroup consisting of kitchen panels, flooring panels, furniture panels,ceiling panels and wall panels.

The decorative panels may further include a sound-absorbing layer. Anexample of such a sound-absorbing layer is disclosed by U.S. Pat. No.8,196,366 (UNILIN).

First Thermoplastic Foils

The first thermoplastic foil includes a thermoplastic foil and an image,usually a colour pattern, printed thereon by inkjet.

There is no real restriction on the content of the colour pattern. Thecolour pattern may also contain information such as text, arrows, logo'sand the like. The advantage of inkjet printing is that such informationcan be printed at low volume without extra cost, contrary to gravureprinting.

In a preferred embodiment, the colour pattern is a wood reproduction ora stone reproduction, but it may also be a fantasy or creative pattern,such as an ancient world map or a geometrical pattern, or even a singlecolour for making, for example, a floor consisting of black and redtiles or a single colour furniture door.

An advantage of printing a wood colour pattern is that a floor can bemanufactured imitating besides oak, pine and beech, also very expensivewood like black walnut which would normally not be available for housedecoration.

An advantage of printing a stone colour pattern is that a floor can bemanufactured which is an exact imitation of a stone floor, but withoutthe cold feeling when walking barefooted on it and being easyreplaceable over time according to fashion.

The first thermoplastic foil preferably has a thickness of at least 80μm. When the inkjet image is printed on a transparent thermoplastic foilused as a protective outer layer of the decorative laminate, itpreferably has a thickness of more than 100 μm, more preferably 200 to700 μm, and most preferably 300 to 500 μm.

If the first thermoplastic foil is used as a protective outer layer ofthe decorative laminate, it may include additional finishing layers onit surface as described here below for the second thermoplastic foil.

Second Thermoplastic Foils

The second thermoplastic foil carries a layer contains avinylchloride-vinylacetate-vinylalcohol copolymer. Such a layer assuresoptimal adhesion to the inkjet printed image while the flexibility canbe maximized by using pigmented free radical UV curable inkjet inkshaving high amounts compounds with one ethylenically unsaturatedpolymerizable group in the polymerizable composition of the inkjet inks.The layer preferably includes a vinylchloride-vinylacetate-vinylalcoholcopolymer containing more than 80 wt % of vinyl chloride and 1 to 15 wt% of vinylalcohol on the total weight of the copolymer. Anotheradvantage of including the vinylalcohol in the specificvinylchloride-vinylacetate copolymer is that the layer becomes not tackyand the second thermoplastic foil can be stored as a roll withoutcausing issues of stickiness.

The application of the layer containing avinylchloride-vinylacetate-vinylalcohol copolymer is preferablyperformed using a coating technique selected from spray coating, dipcoating, knife coating, extrusion coating, spin coating, slide hoppercoating and curtain coating.

The layer containing a vinylchloride-vinylacetate-vinylalcohol copolymeris applied to have a dry weight of preferably 1 to 10 g/m², morepreferably 2 to 7 g/m², and most preferably 3 to 6 g/m². Less than 1g/m² did not provide good adhesion, while above 10 g/m² problems oftackiness and stickiness could again be observed. A very consistentquality was obtained when coated at a dry weight of 2 to 6 g/m².

A coating solution of the vinylchloride-vinylacetate-vinylalcoholcopolymer is preferably made using an organic solvent having a boilingpoint of no more than 95° C. at normal pressure. This allows for fastdrying which is especially needed in a set-up of a single-pass inkjetprinting process. The organic solvent for thevinylchloride-vinylacetate-vinylalcohol copolymer is preferably selectedfrom methyl ethyl ketone or ethyl acetate for minimizing explosion risk.

The second thermoplastic foil is preferably used in the decorativelaminate as the outer layer, thus forming a transparent protective layerfor the viewable inkjet image. However, additional finishing layers maybe applied upon the protective layer.

In a preferred embodiment, an antistatic layer is applied on theprotective layer. Techniques to render decorative panels antistatic arewell-known in the art of decorative laminates as exemplified by EP1567334 A (FLOORING IND).

In a particular preferred embodiment, the decorative panel has apolyurethane finishing layer on the protective layer.

The top surface of the decorative surface, i.e. at least the protectivelayer, is preferably provided with a relief matching the colour pattern,such as for example the wood grain, cracks and knots in a woodprint.Embossing techniques to accomplish such relief are well-known in the artof flooring panels as disclosed by, for example, EP 1290290 A (FLOORINGIND), US 2006144004 (UNILIN), EP 1711353 A (FLOORING IND) and US2010192793 (FLOORING IND).

Most preferably the relief is formed by pressing a digital embossingplate, roll or belt against the thermoplastic foil forming theprotective layer during heat-pressing.

A digital embossing plate is a plate which comprises elevations that canbe used to form a relief on decorative panel by pressing the digitalembossing plate against the protective layer of the decorative panel ornested decorative panels. The elevations may be cured inkjet droplets,jetted by an inkjet print device, and most preferably UV cured inkjetdroplets. The elevations are preferably formed by printing and curinginkjet droplets on top of already cured or pin-cured inkjet droplets.The plate is preferably stiff by using metal or hard plastic.

An alternative of a digital embossing plate may be a digital embossingcylinder which is a cylinder that comprises the elevations to form arelief on decorative panels by pressing and rotating the digitalembossing cylinder against the protective layer of the decorativepanels.

A finishing layer, preferably a polyurethane finishing layer, mayinclude hard particles, like corundum, for preventing scratching of thetop surface. The total quantity of hard particles is preferably between1 g/m² and 100 g/m², preferably 2 g/m² to 50 g/m².

Preferred hard particles are ceramic or mineral particles chosen fromthe group of aluminium oxide, silicon carbide, silicon oxide, siliconnitride, tungsten carbide, boron carbide, and titanium dioxide, or fromany other metal oxide, metal carbide, metal nitride or metalcarbonitride. The most preferred hard particles are corundum andso-called Sialon ceramics. In principle, a variety of particles may beused. Of course, also any mixture of the above-mentioned hard particlesmay be applied.

The amount of hard particles may determined in function of the desiredscratch resistance.

Hard particles having an average particle size of between 1 and 200 μmare preferred. Preferably an amount of such particles of between 1 and40 g/m² is applied above the printed pattern. An amount lower than 20g/m² can suffice for the lower qualities.

The second thermoplastic foil preferably has a thickness of at least 80μm. When the second thermoplastic foil is used as a protective outerlayer of the decorative laminate, it preferably has a thickness of morethan 100 μm, more preferably 200 to 700 μm, and most preferably 300 to500 μm.

Base Layers

In a preferred embodiment, the decorative panel (22) includes a baselayer (35). The base layer provides sufficient rigidness to thedecorative panel, so that when e.g. a long rectangular decorative panelbends under its own weight, the panel does not break. For this reason,the base layer is preferably reinforced with fibres.

In a decorative surface (22), the base layer (21, 35) is attached to theside of the opaque thermoplastic foil of the first and secondthermoplastic foils or attached to the side of a transparentthermoplastic foil if both the first and second thermoplastic foils aretransparent thermoplastic foils.

In a preferred embodiment, the base layer (35) includes substantiallypolyvinyl chloride and reinforcing fibres. More preferably, the baselayer includes substantially polyvinyl chloride and glass fibres.

The base layer may be composed of two foils, preferably polyvinylchloride foils, interposed by a glass fibre fleece.

The base layer may contain mineral. Particularly suitable herein are astalc or calcium carbonate (chalk), aluminum oxide, silica. The baselayer may include a flame retardant.

The base layer may also be a so-called woodplastic composite (WPC),preferably containing one or more polymers or copolymers selected fromthe group consisting polypropylene, polyethylene and polyvinyl chloride.

Pigmented Free Radical UV Curable Inkjet Inks

The colour pattern is printed using one or more pigmented free radicalUV curable inkjet inks containing a polymerizable composition having:

30 to 90 wt % of one or more compounds with one ethylenicallyunsaturated polymerizable group; 10 to 70 wt % of one or more compoundswith two ethylenically unsaturated polymerizable groups; and

0 to 10 wt % of one or more compounds with three or more ethylenicallyunsaturated polymerizable groups, wherein all weight percentages wt %are based upon the total weight of the polymerizable composition.

In a particularly preferred embodiment, the amount of one or morecompounds with one ethylenically unsaturated polymerizable group islarger than 72 wt %, more preferably larger than 80 wt %, wherein theweight percentage wt % is based on the total weight of the polymerizablecomposition.

In a preferred embodiment, the polymerizable compounds consist for morethan 80 wt %, preferably more than 90 wt % of acrylates and optionalN-vinyl lactams, wherein the weight percentage wt % is based on thetotal weight of the polymerizable composition. Such inkjet inks exhibita high curing speed and are especially useful for UV LED curing.

In the most preferred embodiment, the inkjet inks do not containintentionally added water or organic solvents, but may contain a verysmall amount of water, generally less than 5 wt % of water based on thetotal weight of the ink. This water was not intentionally added but cameinto the formulation via other components as a contamination, such asfor example polar organic solvents. Higher amounts of water than 5 wt %of water based on the total weight of the ink often makes the inkjetinks instable, preferably the water content is less than 1 wt % based onthe total weight of the ink and most preferably no water at all ispresent.

In a less preferred embodiment, the pigmented UV curable inkjet inkcontains 20 to 60 wt % of organic solvent based on the total weight ofthe inkjet ink. In such a case, besides the UV curing means extra dryingmeans for solvent evaporation becomes necessary.

The inkjet inks are composed into an inkjet ink set having differentlycoloured inkjet inks. The inkjet ink set may be a standard CMYK ink set,but is preferably a CRYK ink set wherein the magenta (M) ink is replacedby red (R) inkjet ink. The use of a red inkjet ink enhances the colourgamut for wood based colour patterns, which represent the majority ofdecorative panels in flooring.

The inkjet ink set may be extended with extra inks such as brown,magenta, red, green, blue, and/or orange to further enlarge the colourgamut of the ink set. The inkjet ink set may also be extended by thecombination of the full density inkjet inks with light density inkjetinks. The combination of such dark and light colour inks and/or blackand grey inks improves the image quality by a lowered graininess.However preferably the inkjet ink set consists of no more than 3 or 4inkjet inks, allowing the design of single pass inkjet printers of highthroughput at acceptable cost.

In addition to the polymerizable compounds, the pigmented free radicalUV curable inkjet inks include one or more photoinitiators, one or moreco-initiators, one or more inhibitors and one or more surfactants inamounts that are desired to be jettable and curable by inkjet printers.

In a preferred embodiment, the monofunctional polymerizable compoundsconsist of monoacrylates and optionally N vinyl lactams. Usingmonoacrylates and vinyllactams instead of e.g. methacrylates allows forhigh curing speeds.

The pigmented UV curable inkjet ink is a free radical curable inkjetink. It was found in industrial inkjet printing systems thatcationically curable inkjet inks posed problems of jetting reliabilitydue to UV stray light. The UV-curing of the ink caused reflections of UVlight, including UV light hitting the nozzle plate of an inkjet printhead and resulting into failing nozzles due to clogging by cured ink inthe nozzle. Unlike free radical ink where radical species have a muchshorter lifetime, the cationic curable ink continues to cure once anacid species has been generated by UV light in the nozzle.

Polymerizable Compounds

The polymerizable compounds are preferably present in the pigmented UVcurable inkjet inks in an amount of at least 60 wt %, more preferably atleast 70 wt %, wherein the wt % is based on the total weight of theinkjet ink.

Any monomer and oligomer capable of free radical polymerization may beused as polymerizable compound. The viscosity of the UV curable inkjetink can be adjusted by varying the ratio between the monomers andoligomers. The polymerizable compounds may be any monomer and/oroligomer found in the Polymer Handbook Vol 1+2, 4th edition, edited byJ. BRANDRUP et al., Wiley-Interscience, 1999.

The ethylenically unsaturated polymerizable group si preferably selectedfrom the group consisting of an acrylate, a methacrylate, an acrylamide,a methacrylamide, a styrene group, a maleate, a fumarate, an itaconate,a vinyl ether, a vinyl ester, an allyl ether and an allyl ester.

In a preferred embodiment, the polymerizable compounds with oneethylenically unsaturated polymerizable group are selected from acrylicacid, methacrylic acid, maleic acid (or there salts), maleic anhydride,alkyl(meth)acrylates (linear, branched and cycloalkyl) such asmethyl(meth)acrylate, n-butyl(meth)acrylate, tert-butyl(meth)acrylate,cyclohexyl(meth)acrylate, and 2-ethylhexyl(meth)acrylate;aryl(meth)acrylates such as benzyl(meth)acrylate, andphenyl(meth)acrylate; hydroxyalkyl(meth)acrylates such ashydroxyethyl(meth)acrylate, and hydroxypropyl(meth)acrylate;(meth)acrylates with other types of functionalities (e.g. oxiranes,amino, fluoro, polyethylene oxide, phosphate substituted) such asglycidyl (meth)acrylate, dimethylaminoethyl(meth)acrylate,trifluoroethyl acrylate, methoxypolyethyleneglycol (meth)acrylate, andtripropyleneglycol (meth)acrylate phosphate; allyl derivatives such asallyl glycidyl ether; styrenics such as styrene, 4-methylstyrene,4-hydroxystyrene, 4-acetostyrene, and styrenesulfonic acid;(meth)acrylonitrile; (meth)acrylamides (including N-mono andN,N-disubstituted) such as N-benzyl (meth)acrylamide; maleimides such asN-phenyl maleimide; vinyl derivatives such as vinylcaprolactam,vinylpyrrolidone, vinylimidazole, vinylnapthalene, and vinyl halides;vinylethers such as vinylmethyl ether; vinylesters of carboxylic acidssuch as vinylacetate, vinylbutyrate, and vinyl benzoate.

In a more preferred embodiment, the polymerizable compounds with oneethylenically unsaturated polymerizable group are selected frommonoacrylates and vinyllactams.

N-Vinyl lactams are well-known monomers in the art and a detaileddescription is therefore not required. N-Vinyl lactams have a vinylgroup attached to the nitrogen atom of an amide group which may befurther substituted in an analogous manner to the (meth)acrylatemonomers. Preferred examples are N-vinyl caprolactam (NVC) and N-vinylpyrrolidone (NVP), with NVC being particularly preferred.

In a preferred embodiment, the polymerizable compounds with oneethylenically unsaturated polymerizable group include at least oneacyclic-hydrocarbon monofunctional acrylate monomer, preferably selectedfrom octadecyl acrylate (ODA), tridecyl acrylate (TDA), isodecylacrylate (IDA), lauryl acrylate (LA).

In a preferred embodiment, the polymerizable compounds with two or moreethylenically unsaturated polymerizable groups are selected from thegroup consisting of triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol diacrylate, dipropylene glycoldiacrylate, tripropylene glycol diacrylate, polypropylene glycoldiacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate,1,9-nonanediol diacrylate, neopentyl glycol diacrylate,dimethylol-tricyclodecane diacrylate, bisphenol A EO (ethylene oxide)adduct diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate,hydroxypivalate neopentyl glycol diacrylate, propoxylated neopentylglycol diacrylate, alkoxylated dimethyloltricyclodecane diacrylate andpolytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EOmodified trimethylolpropane triacrylate, tri (propylene glycol)triacrylate, caprolactone modified trimethylolpropane triacrylate,pentaerythritol triacrylate, pentaerithritol tetraacrylate,pentaerythritolethoxy tetraacrylate, dipentaerythritol hexaacrylate,ditrimethylolpropane tetraacrylate, glycerinpropoxy triacrylate,alkoxylated cyclohexanone dimethanol diacrylate, caprolactam modifieddipentaerythritol hexaacrylate, alkoxylated cyclohexanone dimethanoldiacrylate, alkoxylated hexanediol diacrylate, dioxane glycoldiacrylate, dioxane glycol diacrylate, cyclohexanone dimethanoldiacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate,vinylether acrylates, propoxylated glycerine triacrylate andpropoxylated trimethylolpropane triacrylate, di-trimethylolpropanetetraacrylate, dipentaerythritol pentaacrylate, ethoxylatedpentaeryhtitol tetraacrylate, methoxylated glycol acrylates and acrylateesters.

Preferred vinylether acrylates are those disclosed in U.S. Pat. No.6,310,115 (AGFA). A particularly preferred compound is2-(2-vinyloxyethoxy)ethyl acrylate. Other suitable vinylether acrylatesare those disclosed in columns 3 and 4 of U.S. Pat. No. 6,767,980 B(NIPPON SHOKUBAI).

Colorants

The colour pigments may be black, cyan, magenta, yellow, red, orange,violet, blue, green, brown, mixtures thereof, and the like. A colourpigment may be chosen from those disclosed by HERBST, Willy, et al.Industrial Organic Pigments, Production, Properties, Applications. 3rdedition. Wiley-VCH, 2004. ISBN 3527305769.

A particularly preferred pigment for a cyan inkjet ink is a copperphthalocyanine pigment, more preferably C.I. Pigment Blue 15:3 or C.I.Pigment Blue 15:4.

Particularly preferred pigments for a red or magenta inkjet ink are C.I.Pigment Violet 19, C.I Pigment Red 254, C.I. Pigment Red 176, C.I.Pigment Red 202 and C.I. Pigment Red 122, and mixed crystals thereof.

Particularly preferred pigments for yellow inkjet ink are C.I PigmentYellow 150, C.I. Pigment Yellow 155, C.I. Pigment Yellow 120 and C.I.Pigment Yellow 180, and mixed crystals thereof.

For the black ink, suitable pigment materials include carbon blacks suchas Regal™ 400R, Mogul™ L, Elftex™ 320 from Cabot Co., or Carbon BlackFW18, Special Black™ 250, Special Black™ 350, Special Black™ 550,Printex™ 25, Printex™ 35, Printex™ 55, Printex™ 90, Printex™ 150T fromDEGUSSA Co., MA8 from MITSUBISHI CHEMICAL Co., and C.I. Pigment Black 7and C.I. Pigment Black 11.

Also mixed crystals may be used. Mixed crystals are also referred to assolid solutions. For example, under certain conditions differentquinacridones mix with each other to form solid solutions, which arequite different from both physical mixtures of the compounds and fromthe compounds themselves. In a solid solution, the molecules of thecomponents enter into the same crystal lattice, usually, but not always,that of one of the components. The x-ray diffraction pattern of theresulting crystalline solid is characteristic of that solid and can beclearly differentiated from the pattern of a physical mixture of thesame components in the same proportion. In such physical mixtures, thex-ray pattern of each of the components can be distinguished, and thedisappearance of many of these lines is one of the criteria of theformation of solid solutions. A commercially available example isCinquasia™ Magenta RT-355-D from Ciba Specialty Chemicals.

Also mixtures of pigments may be used. For example, a black inkjet inkmay include a carbon black pigment and at least one pigment selectedfrom the group consisting of a blue pigment, a cyan pigment, a magentapigment and a red pigment. It was found that such a black inkjet inkallowed easier and better colour management for wood colours.

The pigment particles in the pigmented inkjet ink should be sufficientlysmall to permit free flow of the ink through the inkjet printing device,especially at the ejecting nozzles. It is also desirable to use smallparticles for maximum colour strength and to slow down sedimentation.

The average particle size of the pigment in the pigmented inkjet inkshould be between 0.005 μm and 15 μm. Preferably the average pigmentparticle size is between 0.005 and 5 μm, more preferably between 0.005and 1 μm, particularly preferably between 0.005 and 0.3 μm and mostpreferably between 0.040 and 0.150 μm.

The pigment is preferably used in the inkjet ink in an amount of 0.1 to20 wt %, preferably 1 to 10 wt %, and most preferably 2 to 6 wt % basedon the total weight of the pigmented inkjet ink. A pigment concentrationof at least 2 wt % is preferred to reduce the amount of inkjet inkneeded to produce the colour pattern, while a pigment concentrationhigher than 5 wt % reduces the colour gamut for printing the colourpattern with print heads having a nozzle diameter of 20 to 50 μm.

A white inkjet ink preferably includes a pigment with a high refractiveindex, preferably a refractive index greater than 1.60, preferablygreater than 2.00, more preferably greater than 2.50 and most preferablygreater than 2.60. Such white pigments generally have a very coveringpower, i.e. a limited amount of white ink is necessary to hide thecolour and defects of the core layer. The most preferred white pigmentis titanium dioxide.

The white inkjet ink preferably contains the white pigment in an amountof 5 wt % to 30 wt %, more preferably 8 to 25 wt % of white pigmentbased upon the total weight of the white inkjet ink.

The numeric average particle diameter of the white pigment is preferablyfrom 50 to 500 nm, more preferably from 150 to 400 nm, and mostpreferably from 200 to 350 nm. Sufficient hiding power cannot beobtained when the average diameter is less than 50 nm, and the storageability and the jet-out suitability of the ink tend to be degraded whenthe average diameter exceeds 500 nm.

Polymeric Dispersants

Typical polymeric dispersants are copolymers of two monomers but maycontain three, four, five or even more monomers. The properties ofpolymeric dispersants depend on both the nature of the monomers andtheir distribution in the polymer. Copolymeric dispersants preferablyhave the following polymer compositions:

-   -   statistically polymerized monomers (e.g. monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g. monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g. monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g. monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with polymeric side chains attached to the backbone);        and    -   mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable polymeric dispersants are listed in the section on“Dispersants”, more specifically [0064] to [0070] and [0074] to [0077],in EP 1911814 A (AGFA GRAPHICS).

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30000, more preferably between 1500 and 10000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100,000, more preferably smaller than 50,000 andmost preferably smaller than 30,000.

The polymeric dispersant has preferably a polydispersity PD smaller than2, more preferably smaller than 1.75 and most preferably smaller than1.5.

Commercial examples of polymeric dispersants are the following:

-   -   DISPERBYK™ dispersants available from BYK CHEMIE GMBH;    -   SOLSPERSE™ dispersants available from NOVEON;    -   TEGO™ DISPERS™ dispersants from EVONIK;    -   EDAPLAN™ dispersants from MÜNZING CHEMIE;    -   ETHACRYL™ dispersants from LYONDELL;    -   GANEX™ dispersants from ISP;    -   DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;    -   DISPONER™ dispersants from DEUCHEM; and    -   JONCRYL™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include Solsperse™dispersants from NOVEON, Efka™ dispersants from CIBA SPECIALTY CHEMICALSINC and Disperbyk™ dispersants from BYK CHEMIE GMBH. Particularlypreferred dispersants are Solsperse™ 32000, 35000 and 39000 dispersantsfrom NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt%, more preferably 5 to 200 wt %, most preferably 50 to 90 wt % based onthe weight of the pigment.

Photoinitiating System

A photoinitiating system is used for initiating the polymerization ofthe polymerizable composition in the inkjet inks. The photoinitiatingsystem includes one or more photoinitiators and optionally one or moreco-initiators.

The photoinitiator is a free radical initiator. A free radicalphotoinitiator is a chemical compound that initiates polymerization ofmonomers and oligomers when exposed to actinic radiation by theformation of a free radical.

Two types of free radical photoinitiators can be distinguished and usedin the inkjet ink of the present invention. A Norrish Type I initiatoris an initiator which cleaves after excitation, yielding the initiatingradical immediately. A Norrish type II-initiator is a photoinitiatorwhich is activated by actinic radiation and forms free radicals byhydrogen abstraction from a second compound that becomes the actualinitiating free radical. This second compound is called a polymerizationsynergist or co-initiator. Both type I and type II photoinitiators canbe used in the present invention, alone or in combination.

In order to increase the photosensitivity further, the UV curable inkjetink may additionally contain co-initiators. Suitable examples ofco-initiators can be categorized in three groups:

-   -   1. tertiary aliphatic amines such as methyldiethanolamine,        dimethylethanolamine, triethanolamine, triethylamine and        N-methylmorpholine;    -   2. aromatic amines such as amylparadimethylaminobenzoate,        2-n-butoxyethyl-4-(dimethylamino) benzoate,        2-(dimethylamino)ethylbenzoate, ethyl-4-(dimethylamino)benzoate,        and 2-ethylhexyl-4-(dimethylamino)benzoate; and    -   3. (meth)acrylated amines such as dialkylamino        alkyl(meth)acrylates (e.g., diethylaminoethylacrylate) or        N-morpholinoalkyl-(meth)acrylates (e.g.,        N-morpholinoethyl-acrylate).        -   The preferred co-initiators are aminobenzoates.

Suitable photo-initiators are disclosed in CRIVELLO, J. V., et al.VOLUME III: Photoinitiators for Free Radical Cationic. 2nd edition.Edited by BRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998. p.287-294.

Specific examples of photo-initiators may include, but are not limitedto, the following compounds or combinations thereof: benzophenone andsubstituted benzophenones, 1-hydroxycyclohexyl phenyl ketone,thioxanthones such as isopropylthioxanthone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one, benzildimethylketal, bis (2,6-dimethylbenzoyl)-2,4, 4-trimethylpentylphosphineoxide, 2,4,6trimethylbenzoyldiphenylphosphine oxide,2-methyl-1-[4-(methylthio) phenyl]-2-morpholinopropan-1-one,2,2-dimethoxy-1, 2-diphenylethan-1-one or5,7-diiodo-3-butoxy-6-fluorone.

Suitable commercial photo-initiators include Irgacure™ 184, Irgacure™500, Irgacure™ 907, Irgacure™ 369, Irgacure™ 1700, Irgacure™ 651,Irgacure™ 819, Irgacure™ 1000, Irgacure™ 1300, Irgacure™ 1870, Darocur™1173, Darocur™ 2959, Darocur™ 4265 and Darocur™ ITX available from CIBASPECIALTY CHEMICALS, Lucerin™ TPO available from BASF AG, Esacure™KT046, Esacure™ KIP150, Esacure™ KT37 and Esacure™ EDB available fromLAMBERTI, H-Nu™ 470 and H-Nu™ 470X available from SPECTRA GROUP Ltd.

In a preferred embodiment, the photoinitiator is selected from the groupconsisting of non-polymeric multifunctional photoinitiators, oligomericor polymeric photoinitiators and polymerizable photoinitiators. Such adiffusion hindered photoinitiator exhibits a much lower mobility in acured layer of the UV curable inkjet inks than a low molecular weightmonofunctional photoinitiator, such as benzophenone. Including diffusionhindered photoinitiators, and also diffusion hindered co-initiators havea safety advantage for the operator of the inkjet printer.

Most preferably the diffusion hindered photoinitiator is a polymerizablephotoinitiator, preferably having at least one acrylate group. And mostpreferably the diffusion hindered coinitiator is a polymerizablecoinitiator, preferably having at least one acrylate group.

Suitable diffusion hindered photoinitiator may contain one or morephotoinitiating functional groups derived from a Norrish typeI-photoinitiator selected from the group consisting of benzoinethers,benzil ketals, α,α-dialkoxyacetophenones, α-hydroxyalkylphenones,α-aminoalkylphenones, acylphosphine oxides, acylphosphine sulfides,α-haloketones, α-halosulfones and phenylglyoxalates.

A suitable diffusion hindered photoinitiator may contain one or morephotoinitiating functional groups derived from a Norrish typeII-initiator selected from the group consisting of benzophenones,thioxanthones, 1,2-diketones and anthraquinones.

Suitable diffusion hindered photoinitiators are also those disclosed inEP 2053101 A (AGFA GRAPHICS) in paragraphs [0074] and [0075] fordifunctional and multifunctional photoinitiators, in paragraphs [0077]to [0080] for polymeric photoinitiators and in paragraphs [0081] to[0083] for polymerizable photoinitiators.

Other preferred polymerizable photoinitiators are those disclosed in EP2065362 A (AGFA) and EP 2161264 A (AGFA).

A preferred amount of photoinitiator is 0-50 wt %, more preferably0.1-20 wt %, and most preferably 0.3-15 wt % of the total weight of thecurable pigment dispersion or ink.

Preferred diffusion hindered co-initiators are the polymerizableco-initiators disclosed in EP 2053101 A (AGFA GRAPHICS) in paragraphs[0088] and [0097].

Preferred diffusion hindered co-initiators include a polymericco-initiator having a dendritic polymeric architecture, more preferablya hyperbranched polymeric architecture. Preferred hyperbranchedpolymeric co-initiators are those disclosed in US 2006014848 (AGFA).

The UV curable ink preferably comprises the diffusion hinderedco-initiator in an amount of 0.1 to 50 wt %, more preferably in anamount of 0.5 to 25 wt %, most preferably in an amount of 1 to 10 wt %of the total weight of the ink.

Polymerization Inhibitors

The UV curable inkjet ink may contain a polymerization inhibitor.Suitable polymerization inhibitors include phenol type antioxidants,hindered amine light stabilizers, phosphor type antioxidants,hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,and hydroquinone, t-butylcatechol, pyrogallol may also be used.

Suitable commercial inhibitors are, for example, Sumilizer™ GA-80,Sumilizer™ GM and Sumilizer™ GS produced by Sumitomo Chemical Co. Ltd.;Genorad™ 16, Genorad™ 18 and Genorad™ 20 from Rahn AG; Irgastab™ UV10and Irgastab™ UV22, Tinuvin™ 460 and CGS20 from Ciba SpecialtyChemicals; Floorstab™ UV range (UV-1, UV-2, UV-5 and UV-8) fromKromachem Ltd, Additol™ S range (S100, S110, S120 and S130) from CytecSurface Specialties.

Since excessive addition of these polymerization inhibitors will lowerthe ink sensitivity to curing, it is preferred that the amount capableof preventing polymerization is determined prior to blending. The amountof a polymerization inhibitor is preferably lower than 2 wt % based onthe total weight of the inkjet ink.

Surfactants

Surfactants are used in inkjet inks to reduce the surface tension of theink in order to reduce the contact angle on the thermoplastic foil, i.e.to improve the wetting of the foil by the ink. On the other hand, theinkjet ink must meet stringent performance criteria in order to beadequately jettable with high precision, reliability and during anextended period of time. To achieve both wetting of the substrate by theink and high jetting performance, typically, the surface tension of theink is reduced by the addition of one or more surfactants. In the caseof UV curable inkjet inks, however, the surface tension of the inkjetink is not only determined by the amount and type of surfactant, butalso by the polymerizable compounds, the polymeric dispersants and otheradditives in the ink composition.

The surfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionicand are usually added in a total quantity less than 20 wt % based on thetotal weight of the inkjet ink and particularly in a total less than 10wt % based on the total weight of the inkjet ink.

Suitable surfactants include fluorinated surfactants, fatty acid salts,ester salts of a higher alcohol, alkylbenzene sulphonate salts,sulphosuccinate ester salts and phosphate ester salts of a higheralcohol (for example, sodium dodecylbenzenesulphonate and sodiumdioctylsulphosuccinate), ethylene oxide adducts of a higher alcohol,ethylene oxide adducts of an alkylphenol, ethylene oxide adducts of apolyhydric alcohol fatty acid ester, and acetylene glycol and ethyleneoxide adducts thereof (for example, polyoxyethylene nonylphenyl ether,and SURFYNOL™ 104, 104H, 440, 465 and TG available from AIR PRODUCTS &CHEMICALS INC.).

Preferred surfactants include fluoro surfactants (such as fluorinatedhydrocarbons) and silicone surfactants. The silicones are typicallysiloxanes and can be alkoxylated, polyether modified, polyestermodified, polyether modified hydroxy functional, amine modified, epoxymodified and other modifications or combinations thereof. Preferredsiloxanes are polymeric, for example polydimethylsiloxanes.

The fluorinated or silicone compound used as a surfactant may be across-linkable surfactant. Suitable copolymerizable compounds havingsurface-active effects include, for example, polyacrylate copolymers,silicone modified acrylates, silicone modified methacrylates, acrylatedsiloxanes, polyether modified acrylic modified siloxanes, fluorinatedacrylates, and fluorinated methacrylate. These acrylates can be mono-,di-, tri- or higher functional (meth)acrylates.

Depending upon the application a surfactant can be used with a high, lowor intermediate dynamic surface tension. Silicone surfactants aregenerally known to have low dynamic surface tensions while fluorinatedsurfactants are known to have higher dynamic surface tensions.

Silicone surfactants are often preferred in curable inkjet inks,especially the reactive silicone surfactants, which are able to bepolymerized together with the polymerizable compounds during the curingstep.

Examples of useful commercial silicone surfactants are those supplied byBYK CHEMIE GMBH (including BykT-302, 307, 310, 331, 333, 341, 345, 346,347, 348, UV3500, UV3510 and UV3530), those supplied by TEGO CHEMIESERVICE (including Tego Rad™ 2100, 2200N, 2250, 2300, 2500, 2600 and2700), Ebecryl™ 1360 a polysilixone hexaacrylate from CYTEC INDUSTRIESBV and Efka™-3000 series (including Efka™-3232 and Efka™-3883) from EFKACHEMICALS B.V.

Preparation of Inkjet Inks

The preparation of pigmented UV curable inkjet inks is well-known to theskilled person. Preferred methods of preparation are disclosed inparagraphs [0076] to [0085] of WO 2011/069943 (AGFA).

Inkjet Printing Devices

The inkjet inks may be jetted by one or more print heads ejecting smalldroplets of ink in a controlled manner through nozzles onto anink-receiver surface, which is moving relative to the print head(s).

A preferred print head for the inkjet printing system is a piezoelectrichead. Piezoelectric inkjet printing is based on the movement of apiezoelectric ceramic transducer when a voltage is applied thereto. Theapplication of a voltage changes the shape of the piezoelectric ceramictransducer in the print head creating a void, which is then filled withink. When the voltage is again removed, the ceramic expands to itsoriginal shape, ejecting a drop of ink from the print head. However theinkjet printing method according to the present invention is notrestricted to piezoelectric inkjet printing. Other inkjet print headscan be used and include various types, such as a continuous type andthermal, electrostatic and acoustic drop on demand type.

The inkjet print head normally scans back and forth in a transversaldirection across the moving ink-receiver surface. Often the inkjet printhead does not print on the way back. Bi-directional printing ispreferred for obtaining a high areal throughput. Another preferredprinting method is by a “single pass printing process”, which can beperformed by using page wide inkjet print heads or multiple staggeredinkjet print heads which cover the entire width of the ink-receiversurface. In a single pass printing process the inkjet print headsusually remain stationary and the substrate surface is transported underthe inkjet print heads.

UV Curing Devices

The UV curable inkjet inks are cured by exposing them to ultravioletradiation.

In inkjet printing, the curing means may be arranged in combination withthe print head of the inkjet printer, travelling therewith so that thecurable composition is exposed to curing radiation very shortly afterbeen jetted.

In such an arrangement it can be difficult to provide a small enoughradiation source connected to and travelling with the print head.Therefore, a static fixed radiation source may be employed, e.g. asource of curing UV-light, connected to the radiation source by means offlexible radiation conductive means such as a fiber optic bundle or aninternally reflective flexible tube.

Alternatively, the actinic radiation may be supplied from a fixed sourceto the radiation head by an arrangement of mirrors including a mirrorupon the radiation head.

The source of radiation arranged not to move with the print head, mayalso be an elongated radiation source extending transversely across theink-receiver surface to be cured and adjacent the transverse path of theprint head so that the subsequent rows of images formed by the printhead are passed, stepwise or continually, beneath that radiation source.

Any ultraviolet light source, as long as part of the emitted light canbe absorbed by the photo-initiator or photo-initiator system, may beemployed as a radiation source, such as, a high or low pressure mercurylamp, a cold cathode tube, a black light, an ultraviolet LED, anultraviolet laser, and a UV flash light. Of these, the preferred sourceis one exhibiting a relatively long wavelength UV-contribution having adominant wavelength of 300-400 nm. Specifically, a UV-A light source ispreferred due to the reduced light scattering therewith resulting inmore efficient interior curing.

UV radiation is generally classed as UV-A, UV-B, and UV-C as follows:

-   -   UV-A: 400 nm to 320 nm    -   UV-B: 320 nm to 290 nm    -   UV-C: 290 nm to 100 nm.

Furthermore, it is possible to cure the image using, consecutively orsimultaneously, two light sources of differing wavelength orilluminance. For example, the first UV-source can be selected to be richin UV-C, in particular in the range of 260 nm-200 nm. The secondUV-source can then be rich in UV-A, e.g. a gallium-doped lamp, or adifferent lamp high in both UV-A and UV-B. The use of two UV-sources hasbeen found to have advantages e.g. a fast curing speed and a high curingdegree.

For facilitating curing, the inkjet printer often includes one or moreoxygen depletion units. The oxygen depletion units place a blanket ofnitrogen or other relatively inert gas (e.g. CO₂), with adjustableposition and adjustable inert gas concentration, in order to reduce theoxygen concentration in the curing environment. Residual oxygen levelsare usually maintained as low as 200 ppm, but are generally in the rangeof 200 ppm to 1200 ppm.

EXAMPLE

Materials

All materials used in the following examples were readily available fromstandard sources such as Sigma-Aldrich (Belgium) and Acros (Belgium)unless otherwise specified.

PB15:4 is an abbreviation used for a C.I. Pigment Blue 15:4 pigment,available as Hostaperm™ Blue P-BFS from CLARIANT.

S35000 is an abbreviation used for SOLSPERSE™ 35000, apolyethyleneimine-polyester hyperdispersant from LUBRIZOL.

DB162 is an abbreviation used for the polymeric dispersant Disperbyk™162 available from BYK CHEMIE GMBH whereof the solvent mixture of2-methoxy-1-methylethylacetate, xylene and n-butylacetate was removed.The polymeric dispersant is a polyester-polyurethane dispersant on thebasis of caprolacton and toluene diisocyanate having an amine value of13 mg KOH/g, a Mn of about 4,425 and a Mw of about 6,270.

EFKA is a polyacrylate dispersant available as Efka™ 7701 from BASF.

NVC is N-vinyl caprolactam available from BASF BELGIUM, Nev.

IBOA is isobornylacrylate available as Sartomer™ SR506D from ARKEMA.

ACMO is acryloyl morpholine available from RAHN.

IDA is isodecyl acrylate available as Sartomer™ SR395 from SARTOMER.

PEA is 2-phenoxyethyl acrylate available as Sartomer™ SR339C fromARKEMA.

THFA is tetrahydrofurfuryl acrylate available as Sartomer™ SR285 fromARKEMA.

TBCH is 4-tert.butylcyclohexylacrylate available under the trade name ofSartomer™ CD217 from ARKEMA.

EPA is ethoxylated nonylphenol acrylate available as Sartomer™ SR504Dfrom ARKEMA.

Genomer™ 1122 is a monofunctional urethane acrylate from RAHN.

PEG400DA is polyethyleneglycol diacrylate available as Sartomer™ SR344from ARKEMA.

VEEA is 2-(2′-vinyloxyethoxy)ethyl acrylate, a difunctional monomeravailable from NIPPON SHOKUBAI, Japan.

DPGDA is dipropyleneglycoldiacrylate available as Laromer™ DPGDA fromBASF.

MPDA is 3-methyl-1,6-pentanediyl diacrylate available as Sartomer™ SR341from ARKEMA.

TMPTA is trimethylolpropane triacrylate available as Sartomer™ SR351from ARKEMA.

SR9035 is an ethoxylated (15) trimethylolpropane triacrylate containingfifteen ethoxy units having a molecular weight of 956 and available asSartomer™ SR9035 from SARTOMER.

TPO is 2,4,6-Trimethylbenzoyl-diphenyl-phosphineoxide available asOmnirad™ TPO by IGM.

TPO-L is an acylphosphine oxide photoinitiator available as Omnirad™TPO-L from IGM RESINS.

Irgacure™ 819 is a bisacylphosphineoxide photo-initiator available fromBASF.

Darocur™ ITX is an isomeric mixture of 2- and 4-isopropylthioxanthonefrom BASF.

DETX is an abbreviation for Genocure™ DETX, a photo-initiator availablefrom RAHN.

Irgacure™ 184, Irgacure™ 379 and Irgacure™ 907 are photo-initiatorsavailable from BASF.

Benzophenone is available as Omnirad™ BP from IGM RESINS.

PBZ is 4-phenylbenzophenone, a photo-initiator available as Genocure™PBZ from RAHN AG.

EPD is ethyl 4-dimethylaminobenzoate available as Genocure™ EPD fromRAHN AG.

ERA is 2-ethylhexyl 4-dimethylaminobenzoate available as Genocure™ EHAfrom RAHN.

CN963B80 is a difunctional co-initiator available as Sartomer™ CN963B80from ARKEMA.

CN3755 is a diacrylated co-initiator available as Sartomer™ CN3755 fromSARTOMER.

PMF is p-methoxy phenol.

BHT is an abbreviation for 2,6-di-tert.butyl-4-methylphenol(CASRN128-37-0) from ALDRICH CHEMICAL CO.

Cupferron™ AL is aluminum N-nitrosophenylhydroxylamine from WAKOCHEMICALS LTD.

Irgastab™ UV10 is 4-hydroxy-2,2,6,6-tetramethylpiperidinooxy sebacatefrom BASF.

BYK™ UV3510 is a polyethermodified polydimethylsiloxane wetting agentavailable from BYK CHEMIE GMBH.

Tegoglide™ 410 and Tegoglide™ 450 are surfactants from EVONIK.

Silwet™ L7500 is a silicone surfactant available from MOMENTIVEPERFORMANCE MATERIALS.

Solbin™ AL is a vinylchloride-vinylacetate-vinylalcohol copolymer fromNISSIN CHEMICAL CO LTD.

UAGH™ is a vinylchloride-vinylacetate-vinylalcohol copolymer fromUNIVAR.

UMOH™ is a vinylchloride-vinylacetate-vinylalcohol copolymer from WUXIHONGHUI RESIN CO LTD.

Sunvac™ GH is a vinylchloride-vinylacetate-vinylalcohol copolymer fromfrom YANTAI SUNY CHEM INTERNATIONAL CO LTD.

LPOH™ is a vinylchloride-vinylacetate-vinylalcohol copolymer from WUXIHONGHUI RESIN CO LTD.

Solbin™ TA3 is a vinylchloride-vinylacetate-hydroxypropylacrylatecopolymer from NISSIN CHEMICAL CO LTD.

Vinnol™ E22-48A is a vinylchloride-hydroxypropylacrylate copolymer fromWACKER-CHEMIE.

Vinnol™ E15-40A is a vinylchloride-hydroxypropylacrylate copolymer fromWACKER-CHEMIE.

Solbin™ M5 is a vinylchloride-vinylacetate-hydroxyalkylacrylatecopolymer from NISSIN CHEMICAL CO LTD.

P2 is an 80 μm thick opaque white polyvinyl chloride foil.

C3 is a 500 μm thick transparent polyvinyl chloride foil.

Measurement Methods

1. Adhesion

The adhesion was determined by testing the peel strength according toEN431:1994 on a 50 mm wide sample at a speed of 100 mm/min, but with ameasurement angle of 3600. For good adhesion, a peel strength of 75 N isdesired.

TABLE 1 Criterion Evaluation − − less than 20 N − 20 to 59 N + 60 to 74N + + 75 N or more2. Flexibility

A UV curable inkjet ink was coated on a Metamark™ MD5-100 substrateusing a bar coater and a 10 μm wired bar. The coated sample was fullycured using a Fusion DRSE-120 conveyer, equipped with a Fusion VPS/I600lamp (D-bulb), which transported the samples under the UV-lamp on aconveyer belt at a speed of 20 m/min.

The flexibility was determined using a custom built apparatus shown inFIG. 4 for stretching a strip having a width of 1 cm obtained from thecoated sample using a cutter. The strip was mounted between a firstfixed wall and a second wall which could be horizontally deplaced byrotation of a handle.

The strip was elongated from an original length L1 of 5 cm to the lengthL2 at which the strip ruptured. The elongation was calculated as apercentage according to the following mathematical formula:Elongation (%)=(L2−L1/L1)×100

The evaluation of the flexibility was made in accordance with theclassification described in Table 2.

TABLE 2 Classification Observation + + 90% elongation or more + From 30%to less 90% elongation − Less than 30% elongation

Example 1

This example illustrates that a combination of specific pigmented UVcurable inkjet inks in combination with avinylchloride-vinylacetate-vinylalcohol copolymer provided for goodadhesion and high flexibility in heat-pressing of a decorative panelusing polyvinyl chloride foils.

Preparation of Cyan Pigment Dispersion

Pigmented UV curable inkjet inks were made using a cyan pigment PB15:4dispersed according to the following method. The components according toD-1 or D-2 in Table 3 were mixed for 30 minutes using a DISPERLUX™disperser from DISPERLUX S.A.R.L., Luxembourg. The dispersions were thenmilled using a Bachofen DYNOMILL ECM mill filled with 0.4 mm yttriumstabilized zirconia beads (“high wear resistant zirconia grinding media”from TOSOH Co.). The mixtures were circulated over the mill for 2 hours.After milling, the pigment dispersions were discharged over a 1 μmfilter into a vessel.

TABLE 3 wt% of component D-1 D-2 PB15:4 16.00 15.00 Dispersant 16.0010.00 PMF 0.04 0.14 BHT 0.10 0.10 Cupferron ™ AL 0.04 0.04 Monomer 67.8274.82Preparation of Inkjet Inks

Comparative inkjet inks C-1 to C-7 and inventive inkjet inks I-1 to I-3were prepared by combining the components according to Table 4 and Table5. The wt % is based on the total weight of the inkjet ink.

TABLE 4 wt % of Type component C-1 C-2 C-3 C-4 C-5 Pigment PB15:4 3.003.00 3.00 2.50 3.00 Dispersant S35000 3.00 EFKA 2.00 2.00 2.50 DB1623.00 Monomer NVC 13.40 16.64 IBOA 33.29 PEA 14.41 ACMO 17.80 EPA 9.00MPDA 24.50 20.00 DPGDA 37.36 19.56 7.39 0.96 81.27 VEEA 68.37 TMPTA14.00 11.00 4.00 Photoinitiating TPO 2.95 4.95 2.95 4.95 System TPO-L5.00 3.00 Irgacure ™ 4.00 2.00 2.25 819 DETX 4.00 2.00 2.00 Darocur ™ITX 2.00 Irgacure ™ 2.00 379 Irgacure ™ 184 Benzophenone 4.00 PBZ 2.50EPD 5.00 5.00 CN3755 5.00 2.00 3.00 CN963B80 3.00 EHA 3.00 StabilizerPMF 0.01 0.01 0.01 0.05 0.04 BHT 0.02 0.02 0.02 0.12 0.10 Cupferron ™0.01 0.01 0.01 0.04 0.04 AL Irgastab ™ 1.00 0.25 0.50 UV10 SurfactantTegoglide ™ 0.30 410 Byk ™ UV3510 0.10 1.00 0.75 0.10

TABLE 5 wt % of Type component C-6 C-7 I-1 I-2 I-3 Pigment PB15:4 3.003.70 2.00 2.33 2.50 Dispersant S35000 3.00 1.55 2.50 EFKA 1.33 DB1623.70 Monomer NVC 13.00 13.40 9.90 IBOA 18.75 18.95 PEA 12.81 16.35 THFA14.12 IDA 15.00 4.51 10.48 5.00 Genomer ™ 1122 8.58 TBCH 13.92 ACMO 9.98EPA 9.00 PEG400DA 10.00 DPGDA 49.72 20.77 10.64 10.60 VEEA 24.40 56.81SR9035 7.50 14.51 Photoinitiating TPO 2.95 2.95 System TPO-L 4.00Irgacure ™ 819 2.00 2.25 Darocur ™ ITX 5.00 2.00 2.00 2.00 2.00Irgacure ™ 907 4.00 5.00 Irgacure ™ 379 2.00 Irgacure ™ 184 2.00 EPD2.50 2.50 CN3755 6.00 7.00 7.50 CN963B80 4.00 Stabilizer PMF 0.04 0.040.04 0.04 0.01 BHT 0.10 0.10 0.10 0.10 0.02 Cupferron AL 0.04 0.04 0.040.04 0.01 Irgastab ™ UV10 0.30 0.35 Tegoglide ™ 450 0.80 Byk ™ UV35100.10 0.75 Silwet L7500 1.00 1.00

All the inks had a viscosity and surface tension suitable for inkjetprinting.

Manufacturing of Decorative Panel

The inkjet inks were applied on the matt side of a thermoplastic foil P2at a thickness of 10 μm. The samples were UV cured using a FusionDRSE-120 conveyer, equipped with a Fusion VPS/I600 lamp (D-bulb), whichtransported the samples under the UV-lamp on a conveyer belt at a speedof 20 m/min. The maximum output of the lamp was 1.05 J/cm² and a peakintensity of 5.6 W/cm².

A thermoplastic foil C₃ was coated with a solution in MEK of Solbin™ ALto a dry thickness of 3 g/m². The coated thermoplastic foils P2 wereeach combined with a transparent thermoplastic foil C3 by having the inklayer on the foil P2 facing the layer containing thevinylchloride-vinylacetate-vinylalcohol copolymer on the foil C3.Together with a 4 mm thick PVC foil containing glass fibres as a baselayer, the foils P2 and C3 were heat pressed for 1 minute using anembossing plate at a temperature of 200° C. and a pressure of 12 bar andthen cut into a decorative panel.

Evaluation and Results

The heat-pressed samples were evaluated for adhesion and flexibility.The results are shown in Table 6. The compounds with one, two and threeethylenically unsaturated polymerizable groups are represented byrespectively “1=”, “2=” and “3=”, wherein the weight percentages thereofare based upon the total weight of the polymerizable composition.

TABLE 6 wt% of polymerizable compounds Sample 1 = 2 = 3 = FlexibilityAdhesion C-1 0 81 19 − − C-2 38 48 14 − − C-3 0 95 5 − − − C-4 95 14 + + − C-5 0 100 0 − − C-6 18 73 9 + − C-7 25 56 19 + − I-1 87 130 + + + I-2 30 70 0 + + I-3 81 19 0 + + + +

From Table 6, it can be seen that only the pigmented UV curable inkjetinks I-1 to I-3 were capable of delivering decorative panels having thegood flexibility and good adhesion.

Example 2

This example illustrates the effect of the type ofvinylchloride-vinylacetate copolymer on the adhesion when heat-pressingof a decorative panel using polyvinyl chloride foils.

Manufacturing of Decorative Panel

The inkjet inks C-1, I-2 and I-3 were used for preparing decorativepanels in the same manner as disclosed in Example 1, except that thecopolymer Solbin™ AL was replaced by a vinylchloride-vinylacetatecopolymer as disclosed in Table 7.

TABLE 7 Composition copolymer Adhesion Copolymer % VC % VA Type % C-1I-2 I-3 UAGH ™ 92 5 VOH 3 − + + + + UMOH ™ 90 4 VOH 6 − + + + Sunvac ™GH 90 4 VOH 6 − + + + + LPOH ™ 92 3 VOH 5 − + + + + Solbin ™ TA3 83 42-HO-acrylate 13 − − − + Vinnol ™ E22-48A 75 0 2-HO-acrylate 25 − − +Vinnol ™ E15-40A 84 0 2-HO-acrylate 16 − − − Solbin ™ M5 85 14Decarbonic acid 1 − − − −

The vinylchloride (VC)-vinylacetate (VA) copolymer may contain differenttypes of a third monomer. It can be seen in Table 7 that onlyvinylalcohol (VOH) is capable of providing sufficient adhesion with thespecific UV curable inkjet inks according to the invention I-2 and 1-3.Omitting vinylacetate (VA) or including other types of monomer like2-hydroxy acrylate or decarbonic acid result inferior adhesion.

REFERENCE SIGNS LIST

TABLE 8 11 PVC roll manufacturer 12 PVC roll 13 Decor printer 14 Gravureprinting 15 Decorative PVC roll 16 Warehouse PVC rolls 17 Warehousedecorative PVC rolls 18 Floor panel manufacturer 19 Inkjet printing 20Heat pressing 21 Base layer 22 Decorative panel 23 Decorative panel set31 Tongue 32 Groove 33 Transparent thermoplastic foil 34 Transparent oropaque thermoplastic foil 35 Base layer

The invention claimed is:
 1. A method for manufacturing a decorative surface, the method comprising, in order: a) inkjet printing an image on a first thermoplastic foil by jetting and UV curing one or more pigmented free radical UV curable inkjet inks on the first thermoplastic foil; b) applying on the inkjet printed image a second thermoplastic foil including a layer including a vinylchloride-vinylacetate-vinylalcohol copolymer such that the layer faces the inkjet printed image on the first thermoplastic foil; and c) heat pressing the first thermoplastic foil and the second thermoplastic foil into a decorative laminate; wherein at least one of the first thermoplastic foil and the second thermoplastic foil is transparent; and the one or more pigmented free radical UV curable inkjet inks includes a polymerizable composition including: 30 to 90 wt % of one or more compounds with one ethylenically unsaturated polymerizable group; 10 to 70 wt % of one or more compounds with two ethylenically unsaturated polymerizable groups; and 0 to 10 wt % of one or more compounds with three or more ethylenically unsaturated polymerizable groups, and all weight percentages wt % are based on a total weight of the polymerizable composition.
 2. The method according to claim 1, further comprising: d) cutting the decorative laminate to form a decorative panel.
 3. The method according to claim 1, wherein the first thermoplastic foil and the second thermoplastic foil include polyvinyl chloride.
 4. The method according to claim 1, wherein the first thermoplastic foil is transparent.
 5. The method according to claim 1, wherein the first thermoplastic foil is opaque.
 6. The method according to claim 1, wherein the decorative surface includes a base layer; when one of the first thermoplastic foil and the second thermoplastic foil is opaque, the base layer is attached to a side of the opaque thermoplastic foil; and when both of the first thermoplastic foil and the second thermoplastic foil are transparent, the base layer is attached to a side of one of the transparent thermoplastic foils.
 7. The method according to claim 6, wherein the base layer includes polyvinyl chloride and reinforcing fibers.
 8. The method according to claim 7, wherein the reinforcing fibers include glass fibers.
 9. The method according to claim 1, wherein the one or more pigmented free radical UV curable inkjet inks includes at least one monomer selected from a N-vinyl-lactam and an acyclic-hydrocarbon monoacrylate.
 10. The method according to claim 1, wherein the step of heat pressing is performed by preheating the first thermoplastic foil and the second thermoplastic foil to a temperature above 130° C.
 11. The method according to claim 1, wherein the vinylchloride-vinylacetate-vinylalcohol copolymer in the layer includes more than 80 wt % of vinyl chloride and 1 to 15 wt % of vinylalcohol based on a total weight of the copolymer.
 12. The method according to claim 1, wherein the layer including the vinylchloride-vinylacetate-vinylalcohol copolymer has a dry weight of 1 to 10 g/m².
 13. A decorative panel obtained by the method according to claim
 1. 14. The decorative panel according to claim 13, wherein the decorative panel includes a tongue and groove joint that interlocks with another decorative panel.
 15. The decorative panel according to claim 14, further comprising a polyurethane finishing layer on the at least one of the first thermoplastic foil and the second thermoplastic foil that is transparent. 